Ok, just got off a call with an engineering manager and I asked about slicer and what the status is.

So we just released SDK Tools 2 beta 2 but the slicer fix was not included in that. We just released Ext JS 4.1.0 RC2 a few minutes ago and GA will be the next release. Our goal is to have the SDK Tools 2 with slicer working when GA comes out in a few weeks. Currently we don't see any issues preventing this but of course you never know what will creep it's ugly head up.